Electrical heating unit



Feb. 9, 1943. -1 E, SMITH 2,310,325

ELECTRICAL HEATING UNIT Filed DBC. 50, 1937 2 Sheets-Sheet l INVENTOR. JOM /f/vfff wwf ATTORNEY` Feb. 9, 1943. J. E. SMITH ELECTRICAL HEATING UNIT 2 Sheets-Sheet l Filed Dec. 50, 1937 INVENTOR.

Y ATTORNEY.

Patented Feb. 9, 1943 2.310.325 ELECTRICAL HEATING uNrr .mm n smith. mana, N. J.

Application December 3 EClaims.

This invention relates to electrical heating umts of the immersion type adapted for installation in various kinds of vessels for heating the iluid contents thereof.

According to one of the features of this invention, a wire filament is contained in intimate contact with a covering-of ceramic material forming a heating element which is cast within a metallic casing preferably of aluminum or other suitable material having high thermal conductivity.

In former practice heating elements of this type and casing therefor were assembled by inserting the filaments in pre-formed openings in the casing. whereas in the present invention the metallic casing is cast around the heating elements firmly embedding them in the metal, and thus bringing the ceramic coverings into intimate contact with the casing by reason of shrinkage of the metal against the ceramic coverings and the compacting efl'ect resulting from the high pressure produced by such shrinkage. Previously to the casting operation the ceramic material is applied to the filament in plastic form and baked thereon. Thus more rapid transfer of heat is secured from the wire filament to the metallic casing through which it is conducted to the fluid contentsof the vessel. These features contributing to rapid heat transfer have the advantage of enabling the filament to be operated at a relatively low temperature, so that the heating unit has a longer life. It has been found in practice that the filament thus encased :need not be worked at a temperature sumcient to cause it to reach red heat in service.

Another feature contributing to rapid heat transfer is the construction of the metal casing which is as thin as can be conveniently cast around the ceramic coverings oi the heating filaments.

All of the above features immersed heating element to operate at higher electrical densities per square inch of heating surface than prior types of elements. while at the same time permitting the filament itself to be worked at a comparatively low temperature.

According to another feature of this invention, the heating unit is provided with two elements, preferably of different resistance values. whereby the heating unit provides two different heats; although the separate elements may have the same relative values.

According to still another feature of the invention. the heating element is provided with two sets of terminal pins for connection to a service p lug. the arrangement of the pins being such that combine to enable the 0. 1937, Serial No. 182,531

it is not possible to plug in on one terminal of each of two heating filaments contained within the heating element. Also, the arrangement of the terminal pins may be such as to enable the use ci' a special type of plug having clearance grooves to accommodate terminal pins oi another filament not in service.

Usually, according to this invention, when two heating filaments are used in one heating element the respective nlaments and terminal pins are disposed at right angles. but the two laments and their terminal pins might be disposed in parallel side by side relation. The invention is not limited to the use of terminal pins or any particular arrangement thereof, as in some cases such pins may be dispensed with, and connections made directly to the heating filaments in any appropriate manner to meet the requirements of any particular installation.

A further feature in connection with the use of multiple heating laments is an arrangement of terminal pins so that the usual shape of guard may be used giving protection for the pins and allowing the necessary clearance for use of the standard service plug for connection to the source of power.

Another feature of advantage is that this heating device is a self-contained unit which can be readily attached to any heating vessel by merely roviding the necessary opening for its installa- Various other features and advantages of the invention will appear as the description proceeds, reference being made to the accompanying drawings forming a part of this specification, and in which:

Figure l is a side view partly in section of a heating unit according to my invention shown installed in the wall of a vessel,

Fig. 2 is an end view of the terminal portion of the unit,

Fig. 3 a view of the opposite end of the unit.

Fig. 4 a cross-section on the line I-l of Fig. 1,

Fig. 5 a longitudinal section on the line 5-5 of Fig. 1,

Fig. 6 an enlarged cross-sectidnal detail of a connection of the heating filament to a terminal pin.

Fig. 'I a cross-section illustrating parallel arrangement of two heating laments.

Fig. 8 an end view of the terminal portion oi a two filament heating unit having a modified form of guard,

Fig. 9 is a fragmentary cross-section taken on the line 9 8 of Fig. B,

Fig. 10 is an end view of the terminal portion of a single illament heating unit and a further modiiled guard, and

Fig. 1l a fragmentary cross-section on the line II-l l of Fig. 10.

Referring to the drawings. the reference unmeral i indicates a metallic casing preferably of cast aluminum. since this material has been found to possess the requisite thermal conductivity to eil'ect rapid transfer of heat through its walls.

The heating unit is adapted to be mounted in the wall Ii of a fluid-containing tank or other vessel so that the casing I0 will be immersed. For this purpose the casing I0 may be reduced and threaded at one end as indicated at l2 and provided with a shoulder i3, the reduced portion I2 projecting through an opening Il in the wall Il and tightened by a nut II so as to draw the shoulder rmly against the inner face of the wall Il, providing a iuid tight connection and holding the heating unit rigidly in operating position within the tank.

Two heating filaments i6 and i1 formed oi suitable coiled resistance wire are embedded in ceramic or other appropriate electrical insulating material i8 which lls the coils and surrounds and embeds them throughout their length so as to provide heat-conducting and electrical insulating coverings between the laments i6 and i 'l and the body oi' the metallic casing III.

The ends of each of the laments i8 and il are provided with terminal screws I9 which project beyond the threaded end I2 oi' the casing Ill for receiving the screw threaded terminal pins 20 which are tightened against insulating pieces 2i and washers 22 between the anges 23 of the pins 2li and the outer face 2l of the threaded end i2 of the casing.

Preferably the encased ends of the terminal screws I9 are squared as shown at 25 in Fig. 6, and slotted at 26 to receive the ends of the wire lllaments I6 and I1, after which the slotted portions are swaged together to clamp the filaments tightly to the terminal screws.

In the manufacture of the present heating units the wire filaments and their terminal screws embedded in the ceramic material IB, are suitably held in position so as to dispose the filaments at right angles to each other (Figs. 4 and and the metal of the casing i0 is then cast therearound by an appropriate molding operation. A very tight contact is obtained between the metallic body of the casing and the ceramic material surrounding the heating iilaments, resulting from shrinkage of the metal in solidifying around the ceramic material. The metal of the casing l0 may be of the contour shown in Figs. l, 3 and 4, substantially cross shaped in transverse section, and the walls should be as thin as can be conveniently cast so as not to impede rapid transfer of heat from the i'llaments I6 and i1 and through the casing to the fluid to be heated.

The enclosed laments IB and l1 may be designed for different wattages to provide for a low and a high heat in the one unit. or both of the iilaments may be of the same wattage, providing a reserve filament in case one is burned out in use. In either case the filaments may be conveniently supplied with current through the medium of a service plug. For this purpose, the terminal pins 20 are disposed at right angles to each other in the form shown in Fig. 2, and spaced apart to accommodate the standard service plug such as that indicated by dot and dash lines at 21 in Fig. 2.

Here the plug is shown as supplying current to the illament it, whereas the pins connected to the illamenta i'l are out oi' use at opposite sides of the plug in clearance grooves 28 thereof. Obviously, the plug 2l may be connected to the other two terminals, serving the illament I1, by turning the plug at right angles to the position illustrated in Fig. 2, 4but it will be noted that the arrangement of the pins 20 and the distances between the centers thereof is such that it is not possible to plug in on one terminal of each of the two elements I8 and i1.

'I'he arrangement of the terminal pins 2li as employed herein enables the usual terminal guard to be used. Such a guard is shown at 20 in Fig. l, as being provided with an inturned flange l0 to be clamped by the nut l5 against the outer i'ace Ii oi.' the vessel wall il. thereby holding the guard rigidly in place and permitting easy insertion and adjustment of the plug 21 for connection to the respective pairs oi' pins 2l.

A modiiled form of heating element is disclosed in Fig. 7, this being an illustration of the manner in which two heating laments may be disposed in parallel side by side relation within the body of the casing. In this example of the invention the two iilaments are designated lli and 4i. the ceramic material 42, and the metallic casing 43. The sides of the casing may be formed with grooves as shown at Il to reduce the wall thickness adjacent the heating filaments.

In Figs. 8 and 9 there is shown a combined guard and clamping nut 50. 'I'he nut portion 5i is threaded at 52 for reception on the threaded and reduced part 53 oi the metallic casing 54, and is tightened directly against the outer wall of the tank Il. 'I'he guard portion 55 extends outward as an integral part of the nut portion 5I so as to encompass the terminal pins 5B and gives the necessary accessibility for a service plug.

Il' desired, the two heating iilaments may be utilized for simultaneous operation by connecting the terminal pins 5B together as shown at 51 in Fig. 8. By thus bridging these terminal pins the two laments within the casing will be connected in multiple and fed at the same time by the service plug when connected to either part of the terminal pins 56.

Figs. l0 and 1l illustrate a further modiilcation in which a heating unit casing 6U is provided with a pair of screw-threaded lugs 0| formed about the lament ends (not shown) and adapted to project through openings 62 in the tank wall II. Nuts 63 on the lugs 8i draw the end 6l of the casing tightly against the inner surface B5 of the tank wall Il. A guard piece 66 having a flange portion B1 and openings 6B for the lugs 6i, is clamped between the nuts 63 and the outer face 69 of the wall ii providing a rigid connection between all the parts. A pair of terminal pins 'HI project outwardly from the lugs Bi for connection to the usual service plug. Any suitable torm of terminals may be substituted for the pins.

In conclusion, it is to be understood that the invention is capable of various other forms oi construction and modications, and is therefore not to be limited in its applications except as dened in the appended claims.

I claim:

l. A heating unit of the immersion type for connection to a heating vessel, comprising a pair oi' resistance element sections embedded in electrical insulating material, terminal posts connected to the ends of the element sections, said posts having flattened portions embedded in said insulating material and protruding screwthreaded portions, a metallic casing cast around said insulating material, terminal pins carried by the protruding portions of said posts, and insulation between said terminal pins and the adjacent portions of the casing.

2. A heating unit of the immersion type for Yconnection to a heating vessel, comprising a pair of separate heating laments embedded in electrical insulating material and having protruding ends, the filaments being arranged in planes perpendicular to each other with the protruding ends adjacent each other, a metallic casing cast around said insulating material, and pairs of terminal posts connected to the protruding end of the filaments respectively, said casing having a shoulder and a reduced and threaded portion at the terminal end of the unit, said threaded portion extending through an opening in the vessel Wall, a nut on the threaded extension, and a guard surrounding the terminal posts and having a flange between the nut and the outside wall of the vessel, said nut being tightened against said flange to hold the shoulder against the interior face of the vessel Wall and the flange against the outside face of said wall.

3. A heating unit comprising two heating elements of different values and each arranged in a 1oop-shaped core of ceramic material, the cores being` disposed in planes perpendicular to each other, a thin-walled cast aluminum casing surrounding the heating elements to form a heating unit substantially in the shape of a cross in cross-section with the cores respectively embedded in the opposite arms of said casing.

4. In a heating unit a heating element formed of a coil of Wire, terminal pins having squared inner ends with slots therein for respectively receiving the ends of the wire and outer screw threaded ends, ceramic material surrounding and embedding said Wire and the squared and slotted ends of the pins, and a thin-walled cast aluminum casing surrounding the ceramic material.

5. An electrical heating element comprising a pair of separate cores each having a resistance wire filament embedded in electrical insulation material and having terminal members secured to the ends of said filaments and protruding from the insulation material, the cores being formed to be substantially loop-shaped and disposed in planes substantially perpendicular to each other with the protruding terminal members thereof adjacent each other,l a thermally conductive body having a cruciorm portion with said cores respectively embedded in the opposite arms thereof except for the protruding portions of said terminal members, said body also having a round portion adjacent said terminal pins which is screw threaded, and a nut cooperating with said screw threaded portion.

JOHN E. SMITH. 

